The supersonic wave drag of an aircraft is dependent upon the cross-sectional area distribution of the fuselage and wing together. Traditional supersonic aircraft employ a concept known as area-ruling to reduce drag. In area-ruling, the fuselage is often indented or "waisted" at the wing-root location to achieve a smooth combined wing/fuselage cross-sectional area distribution.
The area-ruling method is based on the well-known supersonic slender body (linear) theory. It can be assumed that at large distances from the body, the disturbances are independent of the arrangement of the components of the body, and are only a function of the cross-sectional area distribution. This means that the drag of a wing-fuselage combination can be calculated as though the combination were a body of revolution with an equivalent cross-sectional area.
It is a generally accepted practice among airframe designers that area-ruling must be used to obtain the most desirable configuration to achieve a low supersonic wave drag for a particular Mach number. As stated previously, in order to achieve a smooth cross-sectional area distribution and to minimize the total cross-sectional area, the most common technique is to "indent" the fuselage enough to permit the wing to be added without sharp discontinuities appearing on the cross-sectional area distribution of the configuration.
FIGS. 1A and 1B show the top and side views, respectively, of a waisted fuselage shape of a traditional supersonic transport aircraft that was designed using linear-theory area-ruling in the presence of the wing. This particular configuration was designed to cruise supersonically at M.sub..infin. =2.4. The top view in FIG. 1A most clearly shows the waisting, `W`, of the fuselage in the wing-root region.
Such fuselage "waisting", however, reduces the useable fuselage volume which could be used for either seating additional passengers or carrying additional payload. In addition, the waisting introduces challenges for the fuselage interior layout because the fuselage shape is not constant.
Accordingly, there exists a need for a method for designing a fuselage that does not have a waist, but which still has good supersonic aerodynamic performance. By removing the fuselage waist, and performing optimization using non-linear aerodynamic methods, a configuration with more fuselage volume can be obtained that has increased supersonic aerodynamic performance compared to a traditional supersonic configuration.